5% a year isn't linear growth. It's exponential growth, but with small factor. $1,000,000 a year or 1000 customers a month are linear growth. I'm not sure what exactly OP meant but I've definitely seen cases where there was definitely a non-compounding ROI for marketing efforts, e.g. if the company spent $100K on ads they might get $200K of sales (or $50K :(), but as soon as they stopped the advertising there was no lasting boost to growth. This can lead to really unhealthy investment cycles where money is poured into the company, it's spent on promotion and generates corresponding growth, but as soon as the money is used up growth trails off and another round of investment is needed.
It would be exponential if it was compounding, I stated "Linear growth of 5% a year on small base". As in, a 5% growth on a $100 base each year which would be $105, $110, $115. Contrasted with 5% compounded growth on $100 of $105, $110.25, $115.76.
